Electrically heated vehicle seats have been known since many years. The heating effect is generated by electric current which is supplied through a conductor having a suitable resistivity that ensures the desired degree of heat in the conductor. The resistance wire is positioned be- tween various layers of a textile material or a plastics material, known as carriers, forming a sheet-like heating element. Several such sheet layers are then to be glued together, sandwiching between them the heating wire proper. This is a comparitively expensive process. The finished heating element is then glued to the seat cushion, the latter usually being of foam-moulded construction. The seat cover is then placed on top. Usually, lashing trech are used for tightening the seat cover. This means that at least one such trench is formed in the foam-moulded cushion and the seat cover material is pulled down into the trench. When a sheet is used for the seat cushion this sheet is often also pulled down into the lashing trench, allowing the cover to be pulled down over the sheet. A condition therefor is that the lashing trench is essentially straight. In case the lashing trench is curved and/or several such lashing trenches are used the heater usually is in the form of several separately heated sheets. Obviously, this increases the costs considerably. When the vehicle is exposed to loads considerable shape changes occur in the foam-moulded cushion and usually the lashing trench is compressed laterally. In time this may lead to rupture of the electrical conductor with a result that the heater stops functioning. In case of heaters that are placed in the seat back the problems are similar, although seat backs are exposed to less load. Also in the case of cushions intended for furniture and bed mattresses there might be a need for electric heaters. The problems in connection with these applications are similar in several respects.